As is known, during the construction of a well for the production of hydrocarbons, the continuous reinforcement of its walls, during the deepening of the well, is necessary for preventing it from collapsing. The reinforcing structure, called “casing”, substantially consists of a metallic cylindrical body inserted in the cavity and adhered to the walls of the well by means of cement.
When the well starts production, the oil is recovered by means of a specific tube, known as a production tube or “tubing”. This is a steel pipe which is inserted in the well until it reaches the level of the reservoir. The tubing is held at the well bottom by means of a system having a combined hydraulic and mechanical seal—called “packer”—which forces the oil to rise to the surface inside the tubing, without touching the walls of the casing.
During the lifetime of the well, the tubing and casing are kept under control by means of a set of service elements, for example, pressure sensors, temperature sensors, plugs, flow valves, data communication control units, etc, which are installed during the construction of the well. These service elements, suitably designed, are positioned, for example, in the annulus, on the outer surface of the tubing. However, as, in order to equalize the pressure exerted at the well bottom by the reservoir, the annulus is filled with a liquid, known as completion liquid, with a density ranging from 1.1 to 1.8 kg/l, the maintenance and/or substitution operation of said service elements present in the annulus, is not easy to effect. The completion liquid normally consists of an aqueous solution of inorganic salts.